The present invention relates to an optical information recording medium of recordable/erasable type utilizing a difference in reflectivity or a phase difference of reflected light resulting from a phase-change of the recording layer by irradiation of a laser beam.
Optical disks are classified into a read only memory (ROM) type and a recordable type (including a rewritable type). The read only memory type has already practically been used as a video disk, an audio disk or a disk memory for a large capacity computer.
Typical recordable type disks include disks of pit-forming/deformation type, organic dye type, magneto-optical type and phase-change type. For the pit-forming/deformation type, a recording layer made of e.g. a dye or a low melting point metal such as Te, is employed, and the recording layer is locally heated by irradiation with a laser beam to form pits or irregularities.
For the organic dye type, a recording layer made of a dye or a polymer containing a dye, is employed, so that the reflectivity (or the refractive index) changes between before and after the recording. This type is practically employed as an optical recording medium for recording CD format signals.
The magneto-optical type is designed to carry out recording or erasing by the direction of magnetization of the recording layer and to carry out retrieving by an magneto-optical effect.
On the other hand, the phase-change type is the one which utilizes a phenomenon that the reflectivity or the phase of reflected light changes between before and after the phase change, whereby retrieving is carried out by detecting the difference in the quantity of reflected light without requiring an external magnetic field. As compared with the magneto-optical type, the phase-change type requires no magnet, and the optical system is simple, whereby preparation of a driving system is easy, and such a phase-change type is advantageous also for downsizing and reduction of costs. Further, it has advantages such that recording and erasing can be carried out simply by modulating the power of a laser beam, and a one-beam overwriting operation is thereby possible wherein erasing and re-recording are carried out simultaneously by a single beam.
It is common to employ a thin film of a chalcogen type alloy as the material for the recording layer for such a phase-change recording system. For example, it has been attempted to use a thin film of an alloy of Gexe2x80x94Te type, Gexe2x80x94Sbxe2x80x94Te type, Inxe2x80x94Sbxe2x80x94Te type, Gexe2x80x94Snxe2x80x94Te type or Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te type.
In the one-beam overwriting phase-change recording, it is common to form recording bits by changing a recording layer in a crystalline state to an amorphous state and to carry out erasing by crystallizing the amorphous phase.
However, the recording layer is usually amorphous immediately after its formation. Accordingly, the entire recording layer is crystallized in a short period of time. This step is called initial crystallization or initialization. It is common to carry out the initialization by irradiating a rotating medium with a laser beam focused to have a diameter of from a few tens to a few hundreds xcexcm.
With respect to the above-mentioned Gexe2x80x94Sbxe2x80x94Te type ternary alloy, only a composition close to a GeTexe2x80x94Sb2Te3 pseudo-binary alloy has heretofore attracted an attention and has been practically developed, and a composition close to a Te85Ge15 eutectic composition or a Sb70Te30 eutectic composition has not been practically employed.
Namely, an alloy material close to the eutectic composition has been considered to be unsuitable as a recording layer for an overwritable optical recording medium, since it undergoes phase separation at the time of crystallization, and it has been impossible to crystallize it by heating for a short period of time of less than 100 nsec, although its amorphous-forming ability is high.
For example, even with a Gexe2x80x94Sbxe2x80x94Te type ternary alloy, no practically crystallization speed has been obtained with a composition close to the Te85Ge15 eutectic composition.
On the other hand, in the vicinity of the Sb70Te30 eutectic composition, a binary alloy of SbuTe1xe2x88x92u (0.58 less than u less than 075) is known to be useful for repeated recording and erasing as between the crystalline and amorphous states, although this is an extremely primitive method wherein only a change in reflectance was monitored (U.S. Pat. No. 5,015,548). Further, a study has been made on a compositional range having a third element, particularly Ge, added to Sb70Te30.
However, these methods have a problem that the productivity is low, since the initialization operation is difficult. Accordingly, there has been no practical progress since then with respect to a composition close to the Sb70Te30 eutectic composition.
Accordingly, it has been considered that only a material in the vicinity of a readily initializable intermetallic composition or its pseudo binary alloy exhibits practical properties.
Irrespective of such a conventional belief, the present inventors have re-examined the crystallization/amorphous conversion properties of the medium having a composition in the vicinity of the eutectic composition, and as a result, have found that such a medium exhibits characteristics superior to a medium having a composition in the vicinity of the composition of the above-mentioned intermetallic compound, when the composition, the layer construction, the recording method, etc. are properly combined.
Namely, the present inventors have conducted a study from the viewpoint of the applicability to mark length recording using an optical disk evaluation machine suitable for high density recording.
As a result, it has been found that a recording layer comprising, as the main component, a SbTe alloy in the vicinity of the Sb70Te30 eutectic composition has a difficulty only in the initial crystallization, and once it has been initially crystallized, subsequent recording and erasing can be carried out at an extremely high speed.
Further, it has been found that a GeSbTe ternary alloy and an InSbTe ternary alloy having Ge or In added thereto, exhibits excellent repetitive overwriting properties.
Especially in a combination with a certain specific recording pulse pattern, it has a merit such that deterioration during repetitive overwriting is less than the material in the vicinity of a BeTexe2x80x94Sb2Te3 pseudo-binary alloy or a material in the vicinity of an InGeTexe2x80x94Sb2Te2 pseudo-binary alloy, which is widely used for repetitive overwriting.
It has been also found that these ternary alloys based on Sb70Te30 have higher crystallization temperatures than the Sb70Te30 binary eutectic alloy and thus are excellent in archival stability.
However, these ternary alloys based on Sb70Te30 had a problem that initialization was more difficult than the Sb70Te30 binary eutectic alloy.
Further, the GeSbTe ternary alloy in the vicinity of the above SbTe eutectic composition had a problem that the recording pulse pattern dependency and the linear velocity dependency were large, and when an usual two level modulation pulse pattern was employed, normal overwriting was possible only within a narrow linear velocity range.
Namely, at a low linear velocity such as 2.8 m/s, recrystallization was so remarkable that formation of amorphous marks tended to be impaired. On the other hand, at a high linear velocity, the crystallization speed was inadequate, and erasing tended to be inadequate. Therefore, proper overwriting was possible only within a limited linear velocity range of 2.8 m/sxc2x150%.
It is an object of the present invention solves such problems involved in using a material having a composition in the vicinity of such a eutectic composition and to make the application of such a material to a high density optical recording medium possible.
In a first aspect, the present invention provides:
An optical information recording medium having a multilayer structure comprising at least a lower protective layer, a phase-change type optical recording layer, an upper protective layer and a reflective layer, on a substrate, wherein the phase-change type optical recording layer has a composition of Znxcex31Inxcex41Sb xcex61Texcfx891, where 0.01xe2x89xa6xcex31xe2x89xa60.1, 0.03xe2x89xa6xcex41xe2x89xa60.08, 0.5xe2x89xa6xcex61xe2x89xa60.7, 0.25xe2x89xa6xcfx891xe2x89xa60.4, and xcex31+xcex41+xcex61+xcfx891=1, whereby overwrite recording is carried out by modulation of light intensity of at least strong and weak two levels, so that a crystalline state is an unrecorded state, and an amorphous state is a recorded state; and
An optical information recording medium having a multilayer structure comprising at least a lower protective layer, a phase-change type optical recording layer, an upper protective layer and a reflective layer, on a substrate, wherein the phase-change type optical recording layer has a composition of Znxcex32Inxcex42Maxcex52Sbxcex62Texcfx892, where Ma is at lest one member selected from Sn, Ge, Si and Pb, 0.01xe2x89xa6xcex32xe2x89xa60.1, 0.001xe2x89xa6xcex42xe2x89xa60.1, 0.01xe2x89xa6xcex52xe2x89xa60.1, 0.5xe2x89xa6xcex62xe2x89xa60.7, 0.25xe2x89xa6xcfx892xe2x89xa60.4, 0.03xe2x89xa6xcex42+xcex52xe2x89xa60.15, and xcex32+xcex42+xcex52+xcex62+xcfx892=1, whereby overwrite recording is carried out by modulation of light intensity of at least strong and weak two levels, so that a crystalline state is an unrecorded state, and an amorphous state is a recorded state.
In a second aspect, the present invention provides:
An optical information recording medium having a multilayer structure comprising at least a lower protective layer, a phase-change type optical recording layer, an upper protective layer and a reflective layer, on a substrate, for overwrite recording by modulation of light intensity of at least two levels, so that a crystalline state is an unrecorded state, and an amorphous state is a recorded state, wherein the phase-change type optical recording layer has a composition of MbzGey(SbxTe1xe2x88x92x)1xe2x88x92yxe2x88x92z, where Mb is at least one member selected from Ag and Zn, 0.60xe2x89xa6xxe2x89xa60.85, 0.01xe2x89xa6yxe2x89xa60.20, and 0.01xe2x89xa6zxe2x89xa60.15; and
An optical recording method, which comprises carrying out mark length modulation recording and erasing on such an optical information recording medium by modulating a laser power among at least 3 power levels, wherein to form inter-mark portions, erasing power Pe capable of recrystallizing amorphous mark portions is applied, and to form mark portions having a length nT where T is a clock period and n is an integer of at least 2, writing power Pw and bias power Pb are applied in such a manner that when the time for applying writing power Pw is represented by xcex11T, xcex12T, . . . , xcex1mT, and the time for applying bias power Pb is represented by xcex21T, xcex22T, . . . , xcex2mT, the laser application period is divided into m pulses in a sequence of xcex11T, xcex21T, xcex12T, xcex22T, . . . , xcex1mT, xcex2mT, to satisfy the following formulae:
when 2xe2x89xa6ixe2x89xa6mxe2x88x921, xcex1ixe2x89xa6xcex2i;
m=nxe2x88x92k, where k is an integer of 0xe2x89xa6kxe2x89xa62, provided that nminxe2x88x92kxe2x89xa71, where nmin is the minimum value of n; and
xcex11+xcex21+ . . . +xcex1m+xcex2m=nxe2x88x92j, where j is a real number of 0xe2x89xa6jxe2x89xa62;
and under such conditions that Pw greater than Pe, and 0 less than Pbxe2x89xa60.5Pe, provided that when i=m, 0 less than Pbxe2x89xa6Pe.
In a third aspect, the present invention provides:
An optical information recording medium having a multilayer structure comprising at least a lower protective layer, a phase-change type optical recording layer, an upper protective layer and a reflective layer, on a substrate, wherein the phase-change type optical recording layer has a composition of Gef(SbdTe1xe2x88x92d)1xe2x88x92f, where 0.60xe2x89xa6dxe2x89xa60.85, and 0.01xe2x89xa6fxe2x89xa60.20 and has a thickness of from 15 to 30 nm, the protective layer has a thickness of from 10 to 50 nm, and the reflective layer is made of a metal containing at least 90 atomic % of Au, Ag or Al and has a thickness of from 50 to 500 nm, whereby mark length modulation recording and erasing are carried out by modulating a laser power among at least 3 power levels at a linear velocity of from 1 to 7 m/s, wherein to form inter-mark portions, erasing power Pe capable of recrystallizing amorphous mark portions with irradiation for less than 100 nanoseconds is applied, and to form mark portions having a length nT where T is a clock period and n is an integer of at least 2, writing power Pw and bias power Pb are applied in such a manner that when the time for applying writing power Pw is represented by xcex11T, xcex12T, . . . , xcex1mT, and the time for applying bias power Pb is represented by xcex21T, xcex22T, . . . , xcex2mT, the laser application period is divided into m pulses in a sequence of a xcex11T, xcex21T, xcex12T, xcex22T, . . . , xcex1mT, xcex2mT, to satisfy the following formulae:
when 2xe2x89xa6ixe2x89xa6mxe2x88x921, xcex1ixe2x89xa6xcex2i;
m=nxe2x88x92k, where k is an integer of 0xe2x89xa6kxe2x89xa62, provided that nminxe2x88x92kxe2x89xa71, where nmin is the minimum value of n; and
xcex11+xcex21+ . . . +xcex1m+xcex2m=nxe2x88x92j, where j is a real number of 0xe2x89xa6jxe2x89xa62;
and under such conditions that Pw greater than Pe, and 0 less than Pbxe2x89xa60.5Pe, provided that when i=m, 0 less than Pbxe2x89xa6Pe.